a. Field of the Invention
The present invention relates to an apparatus for converting a stream of signatures, which have been completed with printing and folding and discharged in such a manner that the signatures overlap one another at a predetermined pitch, into divisions each consisting of a predetermined number of signatures as a preliminary step for transporting signatures to a bookbinding step. More particularly, the present invention relates to a signature stacking apparatus of the conversion type in which signatures are vertically loaded onto a guide plate one by one and stacked thereon substantially horizontally. More specifically, the present invention pertains to a signature stacking apparatus including stacking of signatures and techniques accompanying it, that is, means for pressing a signature at a loading section, means for forming a stack of signature, auxiliary means for forming a stack of signatures and means for attaching a panel to each of the front and rear ends of a stack of signatures.
b. Prior Art
There have heretofore been two types of signature stacking method. In one type of conventional method, signatures are loaded vertically and stacked horizontally; in the other type, signatures are loaded horizontally and stacked vertically. The former method has the advantage that the weight of each of the stacked signatures is not loaded on others and it is possible to smoothly and regularly stack signatures on a guide plate by making use of the weight of each signature, but, at the same time, involves the disadvantage that, when each signature consists of a relatively small number of pages or when paper is relatively thin and hence limp, it may be difficult to stand them alone and they may buckle easily to come out of exact register with each other. The former method includes three types of manner of loading signatures onto a stacking section, that is, upward loading, downward loading and gravity-drop loading. In the case of upward loading, since the entire weight of stacked signatures is loaded on a signature loaded thereunder, when the number of stacked signatures is relatively small, there may be irregularities in alignment of signatures, and as the number of stacked signatures increases, various problems may occur, such as folding of edges of signatures and generation of folding marks or scuff marks. In the case of downward loading, a change in the number of stacked signatures leads to a change in the total thickness of the folded sides of signatures, and as the number of stacked signatures increases, the upper surface of the stack of signatures slants to lead to an undesirable slide of stacked signatures. If the number of stacked signatures is limited to a relatively small value in order to prevent such problem, each bale of signatures becomes disadvantageously small and the number of bales increases, resulting in an increase in the amount of consumption of tying bands. In the case of gravity-drop loading, signatures cannot stably be loaded and therefore cannot be stacked regularily. As the operation speed is increased, the degree of irregularity in alignment of signatures becomes considerably high, so that problems such as folding of edges of signatures and generation of folding marks are readily caused.
The applicant of this application has already developed a guide plate described below and filed an application. Namely, as shown in the specification of Japanese Patent Laid-Open No. 135192/1984, a curved guide plate is provided halfway the signature transport path at a position where the path changes from a slanting transport section to a horizontal transport section, in order to cope with a difference in terms of thickness between the upper and lower sides of signatures which results from the fact that signatures to be stacked are arranged with the folded side thereof directed downward and the cut side thereof directed upward.
However, it has been found as the result of many experiments that, although smooth stacking is achieved when the curvature of a stack of signatures, which is formed due to a difference in terms of thickness between the upper and lower sides of the stack, is equal to or greater than that of the curved guide plate, in the case of stacking signatures which have a relatively small difference in terms of thickness between the upper and lower sides thereof and in which, therefore, the above-described former curvature is smaller than the latter curvature, the respective upper portions of the signatures may come into close contact with each other to cause their lower portions to be lifted from the guide plate, and the apparatus therefore lacks general-purpose property although it is excellent as a special purpose machine.
All signatures which are successively loaded onto a stacking section have already been folded, particularly folded double. If the folding angle is obtuse, the stacking density becomes low, which means that the stack of such signatures occupies a relatively large area and is difficult to handle. For this reason, it is preferable that each of the signatures which are to be stacked should be strongly and sharply folded along the folding line, and if signatures are folded sharply, the stacking density can readily be increased.
Japanese Patent Publication No. 7586/1983 teaches that a signature is passed through the area between a pair of pressure rollers which are in uniform contact with each other, thereby uniformly and strongly forming a fold line, and thus reducing the thickness of the signature.
However, the bookbinding step includes a so-called saddle stitching operation in which staple-type stitching wires are driven into signatures along the above-described fold line and two axial end portions of each stitching wire are bent inwardly. In this stitching operation, if the folding angle is exceedingly acute, a cut may be generated along the fold line of the stitched portion, resulting in a reduction in the stitching effectiveness.
Therefore, it is desired to develop a signature pressing means which enables formation of an acute folding angle to increase the stacking density and yet involves no fear of the stitched portion being cut by saddle stitching wires driven thereinto and thus provides improved stitching effectiveness.
Since signatures are loaded onto a plane at a constant position at all times, it is necessary, in order to allow signatures to be smoothly stacked, to enable the whole of the stack of signatures, together with a front retainer, to move forward by a distance corresponding to the thickness of each signature every time a succeeding signature is loaded, thereby providing room for receiving the succeeding signature at the rear end of the growing stack of signatures at all times.
The specification of Japanese Patent Publication No. 7586/1983 discloses a simple structure wherein a stack of signatures is placed on a table and the forward end of the stack is supported by a front retaining weight. This structure, however, provides no room for smoothly receiving a succeeding signature onto the table, and the succeeding signature is forced into the rear end portion of the stack of signatures, thereby transmitting the pressure produced by the insertion of the signature to the front retaining weight on the table, and thus advancing the weight. Accordingly, relatively high frictional resistance occurs, and this prevents an amount of displacement equal to the thickness of the loaded signature from being reliably and accurately transmitted to the weight, resulting in an extreme increase in the internal pressure of the stack itself. Such high internal pressure prevents smooth loading of a new signature and increases the level of friction occurring when a succeeding signature is loaded, which leads to damage to the printed surface, and a signature which is relatively limp cannot be loaded, thus hindering stacking of signatures. In addition, the stacking length of signatures is limited to a considerably small value, and signatures may be stacked irregularly.
In contrast, U.S. Pat. No. 4,172,531 has the arrangement that a plane for stacking signatures is defined by two parallel chain conveyors which are movable forwardly and the two conveyors, together with a front retainer, can be finely advanced. It is therefore possible to simultaneously advance the respective lower ends of signatures placed on the two conveyors.
However, in the above-described arrangement a succeeding signature is loaded downwardly along the rear end of a stack of signatures. Therefore, it is necessary that not only the central portion of the rear end of the stack of signatures but also two lateral edge portions thereof be uniformly advanced. If, when the stack of signatures is advanced, two lateral edge portions of the rear end of the stack are left behind the central portion thereof, the remaining portions will interfere with the leading edge portion of a succeeding signature and thus prevent smooth loading of the following signature.
As a means for preventing this problem, it may readily be conceived to provide four chain conveyors which are conventionally known in order to advance two lateral edge portions of each signature by two outer chain conveyors in the same manner as the central portion thereof.
However, signature stacking apparatuses are preferably designed to have general-purpose property which enables them to cope with variations in width of signatures which are to be stacked. From this point view, the above-described improvement is considered to be unsatisfactory.
In connection with this, U.S. Pat. No. 4,172,531 discloses an apparatus wherein a signature loading belt mechanism is moved parallel backwardly with respect to a front retainer by a distance corresponding to the thickness of a signature to be loaded and an amount of displacement of the mechanism is transmitted to a cam by which a pneumatic valve is selectively opened and closed to control the amount of air supplied to an air motor so that the front retainer is advanced by the operation of the air motor by a distance corresponding to the amount of backward displacement of the belt mechanism and this advancement of the front retainer results in the belt mechanism returning to its initial position.
However, since this apparatus uses a parallel movement mechanism having a relatively large mass and employs a compressed fluid as a working medium, it is unsatisfactory in follow-up capability required in a high-speed repetitive operation, that is, the apparatus lacks rapid and accurate response, which means that it is impossible to obtain a desired effectiveness. Further, loaded signatures are aligned in such a manner that lateral positions thereof are not in exact register with each other, and this irregularity cannot be corrected.
After signatures have been stacked, it is necessary to protect the front and rear ends of the stack of signatures so that they are not bent or folded.
Concerning the protection of the front end of a stack of signatures, the aforementioned Japanese Patent Laid-Open No. 135192/1984 discloses the following technique.
Namely, the front end of a stack of signatures is reliably retained by a front retainer having a panel. However, retaining by the panel cannot be executed from the beginning of the formation of a stack of signatures for various reasons, and the panel awaits arrival of the front end of the stack of signatures at a position halfway the path defined by a guide plate. Accordingly, stacking of signatures proceeds in a state wherein the front end of the stack of signatures is supported by a temporarily retaining means which is constituted by two upstanding rods during the period which begins at the time of starting stacking of signatures and which ends at the time when the front end of the stack reachs the intermediary position.
However, since the front end of the stack of signatures is temporarily retained by two upstanding rods alone, two lateral edge portions of the foremost signatures are turned up forward in response to the stacking pressure as shown in FIG. 26. This turning up phenomenon becomes more noticeable as the degree of limpness of paper increases and the thickness of paper decreases. When the stack of signatures advances to the panel in the above-described turned up state, a signature which defines the front end of the stack or the foremost signatures including it are undesirably folded, and the signatures thus folded are supplied to the bookbinding step, which results in considerable lowering in the quality of books.
Concerning the attachment of a panel to the rear end of a stack of signatures, the applicant of this application has already disclosed a means wherein, as shown in Japanese Patent Laid-Open No. 135192/1984, a stack of signatures is transported by being pushed with a fork-shaped rear retaining and transporting plate and an auxiliary plate is moved toward the rear end of the transported stack in a direction in which the former faces the latter in order to define a gap between the auxiliary plate and the transporting plate, and a panel is inserted into the gap thus formed.
However, since the rear end of the stack of the signatures is pushed by the rear retaining and transporting plate which is substantially constituted by two rods, the portion of the rear end which is between the two rods is caused to bulge rearward; in such case, the maximum thickness of the bulge exceeds the thickness of the transporting plate and this portion projects rearwardly beyond the plate.
Accordingly, when the panel is inserted along such bulged rear end in a direction parallel to the plane of the latter, the leading end of the panel comes into contact with the upper end of the bulged portion of the rear end of the stack of signatures and presses the latter downward. In consequence, the rear end of the stack is depressed downward and crushed to interfere with the downward movement of the panel, so that the panel is stopped in the course of insertion, thus obstructing tying and baling operations carried out thereafter. In addition, the crushed signatures cannot be used and therefore must be discarded wastefully.